Intake manifolds or distributors constitute closed or hollow pieces with complex and multi-compartmented shapes, not generally allowing production in one piece.
Generally, articles of this type are obtained by mutual assembly of a plurality of distinct parts produced separately by moulding, while seeking divisions generating a minimum number of, preferably two, basic parts which are easy to assemble and allow good sealing of the whole to be obtained.
Intake pipes generally consist, owing to their tubular, elongated and curved structure, of elements which are difficult to obtain from one piece by moulding and, therefore, the assembly plane of the manifold or distributor often crosses them or even follows their longitudinal axis.
U.S. Pat. No. 5,636,605 discloses a composite intake manifold including two parts made from thermoplastic material and assembled together, and an additional attached piece positioned within one of the parts prior to assembly of the two parts. The attached piece defines a plurality of pipe portions which cooperate with complementary portions formed in the part housing the attached piece so as to define inlet pipes of the manifold. The pipe portions of the attached piece define longitudinal halves of the respective pipes, and therefore are joined to the complementary portions by longitudinal weldings extending along their whole length.
However, providing assembly joint segments for the manifold in the region of the pipes weakens the constitution of the latter by directly subjecting them to tensions which can occur between the constituent parts of the manifold and does not allow precise local and therefore reliably sealed assembly, the very long assembly joint also extending to other parts or locations of the manifold.
Moreover, when assembly is carried out by a process which generates mould seams (vibration moulding for example), projections or which does not ensure physical continuity of the internal wall of the pipes, the result is a disturbance of the gaseous flow traversing them.